Silodosin is a α1-receptor antagonist developed by Japan, Kissei Pharmaceutical Co., Ltd, and is used clinically to treat dysuria associated with benign prostatic hyperplasia, with chemical name 2,3-dihydro-1-(3-hydroxypropyl)-5[(2R)-2-[2-[2[(2,2,2-trifluoroethoxy)phenyloxy]ethylamino]propyl]-1H-indole-7-carboxamide. the structural formula thereof is shown in the following:

Optically pure silodosin is obtained mainly by performing a chiral resolution of the racemic intermediates produced from different routes in the current literatures. Besides, unsatisfactory reagents are used in some reaction. For example, Europe patent no. EP0600675 disclosed that the racemic intermediate of formula a synthesized by multi-steps from 1-acetylindoline was resolved with tartaric acid to produce the optically pure compound of formula a.

The route for preparing silodosin disclosed in Europe patent no. EP0600675 involves multi-steps (12 steps), the use of expensive platinum oxide, toxic sodium cyanide and inflammable and explosive sodium azide which is unfavorable for the labor and environment protection. Thus, it is not available for industrialization.
China patent application with publication no. CN101759627 also disclosed that the racemic intermediate of formula a synthesized by multi-steps from 1-acetylindoline was resolved with tartaric acid, and then subjected to subsequent steps. Reagents in this process included 2-bromo-propionyl chloride, N-bromosuccinimide and trifluoroacetic acid which was used twice, wherein, 2-bromo-propionyl chloride was difficult to obtain, N-bromosuccinimide participating in radical reaction could form more by-products instead of pure monobromination product, and trifluoroacetic acid would cause serious corrosion to equipment. This process is difficult in operation due to these disadvantages and not favorable for commercial production.
Japan patent application with publication no. JP2002265444 disclosed that the racemic intermediate of formula b produced by multi-steps from indoline was separated using (1R,2S)-(−)-benzylaminocyclohexanemethanol as resolving agent to afford the optically pure compound of formula b:

Resolving agent is expensive and difficult to recover. In order to get product with higher ee value in these separation methods, recrystallization steps should be repeated many times, which will result in big waste of raw materials, economic loss and environmental pollution. Besides, before optically pure compound of formula b was converted into the compound of formula c, amide must be prepared from the compound of formula b, followed by hoffmann degradation. Thus, the disclosed process gives extra steps and lower yield.
